1. Field of the Invention
The present invention relates to a method of fabricating a microscopic focusing grating coupler that is applicable to a subminiature pickup head for a mobile optic disk and, more particularly, to a method of fabricating a focusing grating coupler using a stamper manufactured by an embossing master.
2. Discussion of Related Art
In general, an optical pickup head is applied in the field of an optic disk such as CD, DVD, and etc., and composed of an optic lens manufactured by a transparent material such as a glass and a plastic, and a number of components such as a collimator, a beam splitter, a quarter wave plate, tracking/focusing servo-actuator, a laser diode, photo diodes and etc. Thus, the pickup head of a prior art has disadvantages in view of an access time and a data transfer rate, as compared with a magnetic disk, since it has a large volume and a heavy weight.
As a mass data storage device for a portable information appliance, a subminiature optic disk driver has been studied, as information and communication technology has been developed. Therefore, it is required a new technology that can improve demerits of the conventional pickup head.
As a technology for reducing a size and a weight of the pickup head remarkably, a method for using a focusing grating coupler composed of an optic grating has been proposed, instead of using an objective lens. The focusing grating coupler is comprised of an ultra fine grating that is finer than a wavelength of light, and focuses a laser light to one point, whereby it is possible to reduce a size of a core part in the pickup head to a semiconductor chip size or less, and to improve an access time and a data transfer rate. The focusing grating coupler employs a principle that a laser light incident on a planar waveguide is focused by using a diffractive grating. It could be fabricated in a very small size and serve as an objective lens.
For increasing a recording density of the pickup head, the laser light focused on the focusing grating coupler should have a minimum spot size, and a numerical aperture (NA) of the lens should be increased since the laser light source is fixed. Thus, in the case of using the technology described above, it is possible to increase a lens size to a constant focal length, i.e. a coupling area, or increase a coupling angle. At this time, a minimum space between grating patterns should be maintained 100 nm or less corresponding to a value smaller than a quarter wavelength of the laser light source. Thus, it is required an expensive equipment such as an electron beam lithography system (EBLS) and a high process technology, and needs time and cost-consuming fabrication processes.